2010 Articles

Equatorial paleosecular variation of the geomagnetic field from 0 to 3 Ma lavas from the Galapagos Islands

Kent, Dennis V.; Wang, Huapei; Rochette, Pierre

Complete progressive thermal demagnetization of nearly 400 oriented samples from 58 sites (lava flows) from the Galapagos Islands of Santa Cruz, San Cristobal and Floreana provide data for the statistical characterization of the time-averaged geomagnetic field near the Equator for the past few million years. Estimates of VGP dispersion due to paleosecular variation range from 9.2° to 11.8° depending on site selection criteria; our preferred estimate based on 64 site VGPs (51 accepted from this study and 13 from the 1971 study by Cox) is 11.4° (95% confidence interval 10.2–13.0°), consistent with previous estimates from the Galapagos Islands as well as paleosecular variation Model G, and confirming that angular dispersion of VGPs near the Equator is relatively low. The mean direction is not significantly different from a geocentric axial dipole field when account is taken of southward plate motion over the Galapagos hotspot. Preliminary paleointensity results from a comparison of the natural remanence with a total thermal remanence produced in a lab field of 15 μT on a subset of 321 samples from 48 sites that had relatively small changes in magnetic susceptibility after laboratory heating suggest that the time-averaged field was about 21 μT, or only two-thirds the present strength, in agreement with some other recent estimates.